Telephone system



July l5, 1941. J. wlcKs TELEPHONE SYSTEM Filed April 22, 1940 5 SheetsFSheet 1 July 15, 1941. J. wlcKs 2,249,449

TELEPHONE SYSTEM Filed April 22,'1940 5 sheets-sheet 2 CORD CIRCUIT 2/0 R200 EXCHANGE EXCHANGE zo L203 201 206 0 czz URZUS *62 ro orf/n Pm. sns @RRI F #PST DISTRIBUTOR 66 mvENToR JOHN WICKS BY fwwlwuy. w54 ATTORNEYS July 15, 1941.

J. WICKS TLEPHONE sYsTEM Filed April 22. 1940 5 Sheets-Sheet 3 T0 OTHER SEC SELS ELS.

` SECONMRY SELECTOR GROUP Z SEC/VDRY SELECTOR GROUP l l /CZO SSI Iig 3 rCZ63 A s [C3/6 INVENTOR JOHN WUOKS ATTORN EYS July 15, 1941. J. wlczKs` 2,249,449

TELEPHONE sYsTEM Filed April 22. 1940 5 sheets-sheet 4 ro @THE/2 TRI/NK .(c/Rcwrs GROUP 3 TRUNK CIRCUIT GROUP 3 E' co D I' C/Pcu/T TRUNK ClRCU/T GROUP 2 CORD /RCUI T I {ITO UTHER TRUNK CIRCUITS GROUP 452 c/Rs. f45/ ATTORNEYS July 15, 1941. J. wlcKs y 2,249,449

TELEPHONE SYSTEM A Filed April 22, 1940 5 sheets-sheet 5 /r B PEPAZ'OP POSITION 9/ Patented July 15, 1941 TELEPHONE SYSTEM John Wicks, Oak Park, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application April 22, 1940, Serial No. 330,974

18 Claims.

The present invention relates to telephone systems and more particularly to improved semiautomatic telephone systems of the character of that disclosed and claimed in John Wicks Patent No. 2,167,733, issued August l, 1939.

It is an object of the present invention to provide an improved arrangement for distributing calls to available cord circuits at a number of operator positions at a B switchboard.

Another object of the invention is to provide a call distributing arrangement between a number of operator positions at an A switchboard and a number of operator positions at a B switchboard which comprises an improved switching arrangement including a plurality of primary selectors and a plurality of secondary selectors.

A further object of the invention is to provide in a call distributing arrangement of the character noted, an improved arrangement for controlling the assignment of both the primary and secondary selectors and the cord circuits at the various operator positions at the B switchboard.

The features of the present invention are illustrated as being incorporated in a telephone system comprising a first exchange including an A switchboard provided with a number of operator positions, a second exchange including a B switchboard provided with a number of operator positions, a. plurality of trunk lines extending between the rst exchange and the second exchange, and automatic switching apparatus in the second exchange for routing calls straightforward from the various operator positions at the A switchboard to the various operator positions at the B switchboard.

In accordance with one feature of the invention the telephone system comprises a B switchboard including a plurality of operator positions, a plurality of groups of cord circuits individually associated with the operator positions, a plurality of secondary selectors having access to the cord circuits, means for causing idle ones of the secondary selectors to preselect idle ones of the cord circuits in the various groups of cord circuits, a plurality of primary selectors having access to the secondary selectors, an A switchboard, a plurality of jacks at the A switchboard, a plurality of trunk lines individually associated with the primary selectors and individually terminating in the jacks, and means at the A switchboard for routing a call over any one of the trunk lines by way of the corresponding one of the jacks. Also the system comprises means controlled when a call is routed over one of the trunk lines for causing the associated one of the primary selectors to operate and select an idle one of the secondary selectors which has preselected an idle one of the cord circuits in one of the groups of cord circuits, thereby to route the call on the one trunk line straightforward to the associated operator position at the B switchboard to be answered, means controlled when a call is routed over the one trunk line for rendering busy the one trunk line, means controlled when the one secondary selector is selected by the one primary selector for rendering busy the one secondary selector and the one cord circuit in the one group of cord circuits, a source of tone voltage, and means controlled when all of the secondary selectors are rendered busy for preventing operation of all of the primary selectors and for connecting the source of tone voltage to each idle one of the trunk lines.

In accordance with another feature of the invention the system comprises means at each oi the operator positions at the B switchboard for answering and for extending a call routed thereto, a plurality of normally ineffective blocking means individually associated with the operator positions, each of the blocking means being eli'ective to prevent calls from being routed to the associated operator position, means controlled While a call is being extended from one of the operator positions for rendering eifective the associated one of the blocking means, additional means controlled while a. call is being extended from each of the operator positions for rendering again ineilective each of the blocking means. More particularly, each of the cord circuits in each of the groups of cord circuits includes means for storing a call routed thereover; and the system comprises further means controlled when a call is stored in one of the cord circuits in one of the groups of cord circuits for rendering again effective the associated one of the blocking means, and additional means controlled when a call is stored in one of the cord circuits in each of the groups of cord circuits for preventing operation of the primary selectors and for connecting the source of tone Voltage to each idle one oi the trunk lines.

In accordance with a further feature of the invention the system comprises means controlled when one of the secondary selectors is selected by one of the primary selectors for rendering busy the secondary selector and the one of the cord circuits in one oi the groups of cord circuits preselected by the one secondary selector and for marking against selection each idle one of the secondary selectors which has preselected the one cord circuit, and means including a distributor controlled when only a predetermined number of the secondary selectors are marked for selection for causing operation of the group of idle secondary selectors marked against selection, thereby to cause the last-mentioned group of secondary selectors to preselect idle ones of the cord circuits in the Various groups of cord circuits. More particularly, the distributor is so connected and arranged that the lastmentioned group of secondary selectors is operated sequentially by subgroups in the event the group exceeds a predetermined number and that the last-mentioned group of secondary selectors is operated substantially simultaneously in the event the group does not exceed the predetermined number.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following speciiication taken in connection with the accompanying drawings in which Figure 1 illustrates the general arrangement of a telephone system including two exchanges and embodying the present invention; and Figs. 2 to 5, inclusive, taken together, illustrate the details of the system having incorporated therein the features of the invention, as briefly outlined above.

Description of the apparatus incorporated in the telephone system Referring now more particularly to Fig. 1 of the drawings, the telephone system there illustrated comprises two exchanges Il) and 20 and a number of one-way trunk lines, including the trunk lines TI, T2, T3, T4, etc., extending therebetween. The exchanges I and 2D are of the manual type, each serving a number of subscriber substations, not shown. The exchange I0 comprises an A board provided with a number of A operator positions, including the positions II and I2, and a B board, not shown; while the exchange 20 comprises an A board, not shown, and a B board provided with a number of B operator positions, including the positions 9| and 92. Also the exchange 20 comprises automatic switching apparatus, including a number of groups of primary selectors, and a number of groups of secondary selectors. For example, the rst and second groups of primary selectors respectively include the individual primary selectors PSI, PS2 and PS3, PS4; while the rst and second groups of secondary selectors respectively include the individual secondary selectors SSI, SS2, SS3, SS4 and SSS, SSS, S81, SSB. Further the exchange 20 comprises a number of groups of paired trunk circuits and cord circuits. For example, the ilrst group of paired trunk circuits and cord circuits includes the paired trunk circuits and cord circuits 5I, 1I and 52, 12, etc., individually associated with the first position SI at the B board; while the second group of paired trunk circuits and cord circuits includes the paired trunk circuits and cord circuits 6I, 8| and 62, 82, etc., individually associated with the second position 92 at the B board. Finally, the exchange comprises common equipment 65 associated with each operator position at the B board and with each trunk circuit and a number of distributors including the distributors 66 and 61.

The trunk lines TI, T2, etc., extending between the exchanges I0 and 20 terminate in jacks at the A board in the exchange ID and in the primary selectors in the exchange 20. For example, the trunk line TI terminates in a jack J I at the iirst position Il at the A board in the exchange I0, the jack J I being multipled to other of the positions at the A board, and terminates in the primary selector PSI in the first group of primary selectors in the exchange 20; While the trunk line T2 terminates in a jack J2 at the second position I2 at the A board in the exchange I0, the jack J2 being multipled to other of the positions at the A board, and terminates in the primary selector PS2 in the first group of primary selectors in the exchange 20. Thus it will be understood that each primary selector in each group of primary selectors in the exchange 2B is accessible by way of an associated trunk line to several of the positions at the A board in the exchange I0; and that each position at the A board in the exchange I0 has access by way of the associated trunk lines to several primary selectors in each group of primary selectors in the exchange 2D.

Each secondary selector in each group of secondary selectors in the exchange 20 terminates a trunk line accessible to the primary selectors in a corresponding group of primary selectors. For example, the secondary selectors SSI, SS2 and SS3 in the first group of secondary selectors respectively terminate the trunks 2|, 22 and 23 accessible to the primary selectors in the first group of primary selector while the secondary selectors SS4, etc., in the rlrst group of secondary selectors respectively terminate the trunks 24, etc., accessible to the primary selectors in the second group of primary selectors. Similarly, the secondary selectors SSS, SSB and SS'I in the second group of secondary selectors respectively terminate the trunks 25, 26 and 21 accessible to the primary selectors in the rst group of primary selectors; While the secondary selectors SSB, etc., in the second group of secondary selectors respectively terminate the trunks 28, etc., accessible to the primary selectors in the second group of primary selectors. Thus it will be understood that the primary selectors in each group of primary selectors have access to several secondary selectors in each group of secondary selectors.

Each trunk circuit in each group of trunk circuits in the exchange 20 terminates a trunk accessible to the secondary selectors in a corresponding group of secondary selectors. For example, the trunk circuits 5I and 52 in the rst group of trunk circuits respectively terminate the trunks 3l and 32 accessible to the secondary selectors in the first group of secondary selectors; while other trunk circuits in the first group of trunk circuits respectively terminate the trunks 35, 36, etc., accessible to the secondary selectors in the second group of secondary selectors. Similarly, the trunk circuits 6I and 62 in the second group of trunk circuits respectively terminate the trunks 4I and 42 accessible to the secondary selectors in the iirst group of secondary selectors; while other trunk circuits in the second group of trunk circuits respectively terminate the trunks 45, 46, etc., accessible to the secondary selectors in the second group of secondary selectors. Thus it will be understood that the secondary selectors in each group of secondary selectors have access to a number of trunk circuits in each group of trunk circuits.

Each distributor in the exchange 20 governs the distribution of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the corresponding group of primary selectors and controls the cutuii of the primary selectors in the corresponding gro-up of primary selectors. For example, the first distributor 66 governs the distribution of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the iirst group of primary selectors, and controls the cutoi of the primary selectors in the rst group of primary selectors.

The A board in the exchange I is of conventional connection and arrangement comprising a number of substantially identical operator positions each including position apparatus. As best shown in Fig. 2, the position apparatus at the rst A operator position II comprises position equipment including a number of cord circuits connected and arranged in a manner similar to the cord circuit 2|0. More particularly, the cord circuit 2|0 comprises a line relay R200, a busy relay R205, a call plug P201 and an answer lamp L203, and it is adapted to be connected to the telephone instrument 202 at the first A operator position Also, the jack JI at the iirst A operator position II terminating the trunk line TI has a control relay R2|5 and a busy lamp L204 individually associated therewith.

The B board in the exchange 20 is of conventional connection and arrangement comprising a number of substantially identical operator positions each including position apparatus. As best `shown in Fig. 5, the position apparatus at the rst B operator position 9| comprises position apparatus 93 including a telephone instrument, not shown, a position key K530, an answer relay R535, apparatus for connecting the telephone instrument to any one of the associated cord circuits, not shown, and a number of split relays individually associated with the various cord circuits, the split relay R540 being individually associated with the cord circuit 1|.

Preferably. each of the primary selectors is identical to the primary selector PSI in the first group of primary selectors which comprises, as best shown in Fig. 2, a rotary switch 250 and a number of relays including a line relay R220, a hold relay R230 and a stop relay R240 connected and arranged in a manner more fully described subsequently. The rotary switch 250 comprises four rotary wipers 25|, 253, 255 and 251 provided with individually associated rotary contact banks 252, 254. 256 and 250 and a rotary magnet M259 for moving the wipers noted in the rotary direction.

Preferably, each of the secondary selectors is identical to the secondary selector SSI in the first group of secondary selectors `which comprises, as best shown in Fig. 3, a rotary switch 310, a busy relay R360 and a test relay R365 connected and arranged in a manner more fully described subsequently. The rotary switch 310 comprises four rotary wipers 31|, 313, 315 and 311 provided with individually associated rotary contact banks 312, 314, 316 and 318 and a rotary magnet M319 for moving the wipers noted in the rotary direction.

Preferably, each of the trunk circuits is identical to the trunk circuit 5| in the rst group of trunk circuits, which comprises, as best shown in Fig. 4, a number of relays including a busy relay R420, a control relay R425, an answer relay R430, a switching relay R440, a storage relay R450 and a start relay R460 connected and arranged in a manner more fully described subsequently.

Preferably, each of the cord circuits is identical to the cord circuit 1I in the rst group of cord circuits, which comprises, as best shown in Fig. 5, a repeater 500, and a number of relays including a line relay R520, a battery supply relay R5I0 and a busy relay R525 connected and arranged in a manner more fully described subsequently. Further the cord circuit 1| includes a plug P545 and has individually associated therewith an answer lamp L546 and a line lamp L541.

The common equipment comprises, as best shown in Fig. 4, a number of relays including an operator start relay R405, an operator busy relay R400 and a storage busy relay R4|0, connected and arranged in a manner more fully described subsequently.

Preferably, each oi' the distributors is identical to the iirst distributor 60 which comprises, as best shown in Figs. 2 and 3, a rotary switch 300 and a number of relays, including a common primary selector cutoff relay R265, a hold relay R210, two step relays R215 and R280, a plurality of individual secondary selector cutoi relays, including the individual secondary selector cutoif relay R330 individually associated with the secondary selector SSI in the rst group of secondary selectors, a secondary selector start relay R335, a switching relay R3I0, a test start relay R340, a test stop relay R345, a distributor start relay R350 and a common secondary selector cutoff relay R325 connected and arranged in a manner more fully described subsequently. The rotary switch 300 includes two rotary wipers 30| and 303 provided with individually associated rotary contact banks 302 and 304 and a rotary magnet M305 for moving the wipers noted in the rotary direction.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system will be facilitated from a consideration of the general operation of the various pieces of apparatus incorporated therein incident to the extension of a call from the A board in the exchange I0 to the B board in the exchange 20, as will appear hereinafter.

General operation of the system Considering now the general operation of the system with reference to Fig. 1 of the drawings it is noted that, after a call on a telephone line in the exchange I0 which is to be completed to a telephone line in the exchange 20 is answered by the operator at one oi the operator positions at the A board in the exchange I0, such, for example, as the first A operator position II, the call is trunked by way of one o1' the trunk lines extending between the exchange I0 and the exchange 20, such, for example, as the trunk line TI, to the automatic switching apparatus in the exchange 20. The call is then automatically routed or trunked straightforward by the switching apparatus in the exchange 20 over an idle one of the cord circuits associated with an idle one of the operator positions at the B board, such, for example, as the first B operator position 9|. More particularly, when the operator at the iirst A operator position inserts the call plug of a cord circuit at her position into the jack J I terminating the trunk line TI, operation of the primary selector PSI in the first group of selectors is initiated, whereupon the rst selector PSI seizes an idle trunk in the group of trunks accessible thereto, such, for example, as the trunk 2|. At this point it is noted that the trunk 2| is idle only when the associated secondary selector SSI in the first group of secondary selectors is idle and has previously selected an idle one of the trunks accessible thereto, such, for example, as the trunk 3|, the trunk 3l being marked as idle only when the associated paired trunk circuit 5| and cord circuit 'II are idle and the operator at the first B operator position 9| is idle and in readiness to receive a call. Accordingly, the primary selector PSI operates immediately to seize the trunk 2| extending by way of the secondary selector SSI, the trunk 3|, the trunk circuit 5| and the cord circuit II to the first B operator position 9|, whereupon apparatus at the first B operator position 9| operates to connect the telephone instrument thereat to the cord circuit 1I and to cause a zip-zip tone to be transmitted to the telephone instrument at the first B operator position 0I and over the previously traced connection to the telephone instrument at the first A operator position Il. Accordingly, almost immediately the operator at the first A operator position II in the exchange I0 inserts the call plug of the cord circuit at her position into the jack J I, the connection is completed to the first B operator position 9| in the exchange 20 and tone is heard in the receiver of the telephone instrument at the rst A operator position II indicating to her that the number may be passed to the operator at the first B operator position 9|. The operator at the first A operator position II then passes the number to the operator at the first B operator position 9| whereupon the operator at the first B operator position 9| promptly completes the connection to the called telephone line in the exchange 20, at which time the position apparatus 93 at the first B operator position 9| is again rendered idle for further use.

Idle ones of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in a corresponding group oi primary seiectors are assigned intermittently by the associated distributor. For example, when a predetermined number of the secondary selectors in the various groups of secondary selectors are rendered busy to the primary selectors in the first group of primary selectors, operation of the associated rst distributor 66 is initiated. At this point it is noted that the secondary selectors in the various groups of secondary selectors may be rendered busy either by the direct seizure and extension of connections by way of the secondary selectors or by the seizure and extension of connections by way o! the trunk circuits previously selected by the secondary selectors. Accordingly, when operation of the first distributor 66 is initiated, operations of the idle secondary selectors in the various groups of secondary selectors accessi'- ble to the primary selectors in the first group of primary selectors which are selecting busy trunk circuits are' initiated. These secondary selectors in the various groups of secondary selectors then operate to preselect idle ones of the trunk circuits in the various groups of trunk circuits. Further, it is noted that the particular mode of operation of the first distributor 66 depends upon the number of secondary selectors in the various groups of secondary selectors, the operations of which are initiated when operation of the rst distributor 66 is initiated. More particularly, in the event the operations of a large number of secondary selectors are initiated, the first distributor 66 operates further in order to cause these secondary selectors to be operated in sequential groups; on the other hand, in the event the operations of a small number of secondary selectors are initiated, the first distributor 66 is not further controlled, thereby to allow all of these secondary selectors to operate simultaneously.

Furthermore, the first distributor 66 is so connected and arranged that when all of the secondary selectors in the various groups of secondary selectors, accessible to the primary selectors in the rst group of primary selectors, are busy, the irst distributor 66 operates, thereby to prevent further operation of the primary selectors in the iirst group of primary selectors and to mark as busy the associated trunk lines terminating in the jacks at the various positions at the A board in the exchange I0.

Also the trunk circuits in each group of trunk circuits are so connected and arranged that when the associated B operator position is busy answering a call on a cord circuit in the associated group of cord circuits, each of the other trunk circuits in the associated group of trunk circuits is rendered busy, thereby to prevent additional calls to be extended to the associated B operator position at this time.

Furthermore, the trunk circuits in the various groups of trunk circuits are so connected and arranged that, when all of the B operator positions are busy, one additional call may be stored in a trunk circuit in each group oi' trunk circuits. Finally, the common equipment is so connected and arranged that, when one call is stored in a trunk circuit in each group of trunk circuits, the various distributors are controlled, thereby to prevent operation of the primary selectors in the various groups of primary selectors and to mark as `busy each of the trunk lines extending to the various positions at the A board in the exchange I0.

Detailed operation of the system Considering now the detailed operation of the system with reference to Figs. 2 to 5, inclusive, it is assumed that the operator at the first A operator position II in the exchange I0 has answered a call on the cord circuit 2 I0 which is to be completed in the exchange 20. After answering the call the operator at the first A operator position inserts the cali plug P201 of the cord circuit 2|0 into one of the jacks terminating an idle one of the trunk lines, such, for example, as the jack J l. the trunk line TI being marked as idle by the extinguished condition of the busy lamp L204 associated with the jack J I terminating the trunk line TI. When the call plug P201 is inserted into the jack J I there is completed an obvious circuit for energizing in series the winding of the busy relay R205 in the cord circuit 2I0 and the winding of the control relay R2I5, thereby to cause operation of these relays. Upon operating, the busy relay R205 completes, at the contacts 206, an obvious circuit for illuminating the answer lamp L203; and upon operating, the control relay R2|5 completes, at the contacts 2|6, an obvious circuit for illuminating the busy lamp L204 at the first A operator position I I and the corresponding busy lamps at the other A operator positions. The illumination of the answer lamp L203 indicates to the the control conductor operator positions thereat that the trunk line TI is bus R200 in the cord circuit 2I0, C2 I 2, the call plug P201, the jack J I, the line conductor C295 of the trunk line TI, the contacts 243, the lower Winding of the line relay R220 in the primary selector PSI, the contacts 24|, the line conductor C294 of the trunk line TI, the jack JI, the call plug P201, CZII and the lower winding of the line relay R200 in the cord circuit 2I0 to battery. When this circuit is completed the line relay R220 in the primary selector PSI operates; however, the line relay R200 in the cord circuit 2I0 does not operate due to the high series resistance of this circuit. Upon operating,

the contacts 23|, a path for applying ground potential to the Wiper 255 of the rotary switch 250 and completes, at the contacts 233, a test circuit for the stop relay R240.

'I'he subsequent operation of the primary selector PSI depends upon the idle tion of the 2I |by way of the wiper 251 and engaged contact in the associated contact bank 258 of the rotary switch 250, the contacts 241 and 233, the winding of R240, the contacts 232, C223 and the contacts 266 to ground. The short-circuiting of the winding of the stop relay R240 positively prevents operation thereof at this time. I'he circuit for energizing the rotary magnet M259 extends from the grounded control conductor C264 of the trunk 2| the previously traced path to the contacts 233, and therefrom by way of the contacts 259 and the rotary magnet M259 to battery. When thus of the rotarytswitchl, ,one stepA ,intheelockwise Icause 1the wiper 251,01 the direction I thereby to rotary switch 25,0 to; `eariagethe .wir .the associated eontat .bank 258 terr,niilatine `ef the `next 1 trunk I Ae- Seletor PSI oneratesas second contact cordingly, the primary WWusl EXPIBQQG.

thereby te ,test t the dit 0r busy condition of the next trunk. More particularly, the rotary magnet M259 of the rotary switch 250 is energized intermittently, thereby to cause the rotary step in the clockwise direction until the wipers noted thereof select an idle trunk.

Assuming that the trunk 2| selected by the Wipers noted of the rotary switch 250 is idle at this time, battery potential appears upon the control conductor C264 thereof and there is cominterrupt's, at the contacts 241, the previously mentioned path short-circuiting the rotary magnet M259 and prepares, at the contacts 246, a circuit for energizing in series the Winding of rotary magnet M259, which circuit is completed incident to the switchsecondary selector SSI ter- Y in thel associated contact bant; 318` Vmi the rotary switch 310 to the contra; ,conductor C264 of 1 ithe trunk 2l, `the path 250. the contacts 242,

for applying ground potential to the control con-- ductor C383 of the trunk 3| which is completed depending upon a number of conditions, in a manner more fully explained hereinafter. For example, a path may be completed for applying ground potential to the control conductor C383 of the trunk 3| which extends from ground by way of the contacts 424 to the control conductor C303 of the trunk 3|; a path may be completed for applying ground potential to the control conductor C383 ci the trunk 3| which extends from ground by way of the contacts 44|, 433, and 423 to the control conductor C383 of the trunk 3|; a path may be completed for applying ground potential to the control conductor C383 of the trunk 3| which extends from ground by way of the contacts 454, 432 and 423 to the control conductor C383 of the trunk 3|; and a path may be completed for applying ground potential to the control conductor C383 of the trunk 3| which extends from ground by way of the contacts 462, 453, 432 and 423 to the control conductor C383 of the trunk 3|. The particular one oi' these paths for applying ground potential to the control conductor C383 of the trunk 3| depends upon certain operating conditions of the trunk circuit 5|, the associated cord circuit 1| and the apparatus at the associated first B operator position 9|, in a manner more fully explained hereinafter. Assuming that the secondary selector SSI has previously selected the trunk 3| extending to the trunk circuit 5| at this time, the path for applying battery potential to the control conductor C264 of the trunk 2| extends from battery by way of the winding of the test relay R365, the wiper 315 and engaged contact in the associated contact bank 316 of the rotary switch 310, the control conductor C382 of the trunk 3|,

the contacts 422, 452, 43|, 432 and 423, the control conductor C383 oi the trunk 3| and the wiper 311 and engaged contact in the associated contact bank 318 of the rotary switch 310 to the control conductor C264 of the trunk 2|.

Also upon operating, the stop relay R240 interrupts, at the contacts 24| and 243, the previously traced circuit for energizing the lower winding of the line relay R220, thereby to cause the line relay to restore. Also the stop relay R240 completes, at the contacts 242 and 244, a loop circuit extending between the line relay R200 in the cord circuit 2|0 and the line relay R520 in the cord circuit 1|. This loop circuit extends from ground by way of the upper winding of the line relay R220, C2I2, the call plug P201, the jack JI, the line conductor C295 of the trunk line TI, the contacts 244, the wiper 253 and engaged contact in the associated contact bank 254 of the rotary switch 250, the line conductor C202 of the trunk 2|, the wiper 313 and engaged contact in the associated contact bank 314 of the rotary switch 310, the line conductor C38| of the trunk 3|, the winding 504 of the repeater 500, the right-hand and left-hand windings of the line relay R520, the winding 503 of the repeater 500, the line conductor C380 of the trunk 3|, the wiper 31| and engaged contact in the associated contact bank 312 of the rotary switch 310, the line conductor C280 of the trunk 2|, the wiper 25| and engaged contact in the associated contact bank 252 of the rotary switch the line conductor C294 of the trunk line TI, the jack Jl, the call plug P201, C2|| and the lower winding of the line relav R200 in the cord circuit 2|0 to battery.

When this loop circuit is completed the line relay R520 in the cord circuit 1| operates. However, the line relay R200 in the cord circuit 2|0 does not operate due to the high series resistance oi this circuit.

Upon restoring, the line relay R220 interrupts, at the contacts 22|, the previously mentioned circuit forenergizing the winding oi the hold relay R230, thereby to cause the latter relay to restore shortly thereafter, the hold relay being of the slow-to-release type. At this point it is noted that, prio-r to the restoration of the hold relay R230 to interrupt, at the contacts 23|, the previously traced path for applying ground potential to the control conductor C284 of the trunk 2|, an alternative path is completed for applying ground potential to the control conductor C204 of the trunk 2|. Accordingly, the previously mentioned holding circuit for energizing the winding of the busy relay R360 and the previously traced circuit for energizing in series the winding of the stop relay R240 and the rotary magnet M259 are not interrupted incident to the restoration of the hold relay R230.

Upon operating, the line relay R520 in the cord circuit 1| completes, at the contacts 522, an obvious circuit for illuminating the line lamp L541 and an obvious path for applying ground potential by way of the answer lamp L54B to the control conductor C55| in the position apparatus 93 at the first B operator position 0|. This application of ground potential to the control conductor C55|' causes the position apparatus 93 to operate, thereby to associate the telephone instrument at the iirst B operator position 9| with the cord circuit 1|, whereupon a circuit is completed for illuminating intermittently the answer lamp L54E. The illumination of the line lamp L541 indicates to the operator at the first B operator position 9| that there is a call waiting to be answered on the cord circuit 1|; while the flashing of the answer lamp L54B indicates to the operator at the first B operator position 9| that the position apparatus 93 is operatively connected to the cord circuit 1|. Also when the position apparatus 93 is operatively connected to the cord circuit 1|, tone current is transmitted therefrom to the telephone instrument at the iirst B operator position 9| and over the line conductors C550 and C55| to the repeater 500. More particularly, tone current is transmitted over the windings 50| and 502 of the repeater 500, thereby to cause a similar tone current to be transmitted over the previously traced connection, including the trunk line T|, to the cord circuit 2 0 at the first A operator position The transmission of tone current to the receiver of the telephone instrument at the rst B operator position 9| indicates to the operator thereat that the position apparatus 93 is operatively connected to one of the cord circuits; while the transmission of tone current to the cord. circuit 2|0, and consequently to the telephone instrument 202 operatively associated therewith at the first A operator position indicates to the operator thereat that the call has been answered at the B board in the exchange 20. Accordingly, the operator at the first A operator position I| in the exchange |0 passes the number to the operator at. the first B operator position 0| in the exchange 20; and thereafter the operator at the first B operator position 0| completes the connection to the called telephone line in the exchange 20.

Also when the position apparatus 93 is connected te the cord circuit the answer relay R535 operates, thereby to complete, at the contacts 53,6, an obvious multiple circuit for energizing the windings of the answer relays in the trunk circuits in the first group of trunk circuits. For example, the answer relay R430 in the trunk circuit is operated, thereby to complete, at the contacts 433, the previously traced path for applying ,ground potential to the control conductor C383 of the trunk 3|. Similarly. the answer relays in the other trunk circuits in the iirsty group of trunk circuits operate, thereby to mark the trunks respectively extending thereto as busy in order to prevent the secondary selectors in the various groups of secondary selectors which have previously selected the trunks mentioned from being selected by the primary selectors in the various groups of primary selectors at this time, in order to mark the other cord circuits in the first group of cord circuits individually associated with the first B operator position 9| as busy to the primary selectors in the various groups of primary selectors.

Also upon operating, the line relay R520 in the cord circuit 'II completes, at the contacts 52|, an obvious circuit for energizing the winding of the busy relay R525, thereby to cause the latter relay to operate. Upon operating, the busy relay R525 completes, at the contacts 526, an obvious circuit for energizing the winding of the busy relay R420 in the trunk circuit 5|, thereby to cause the latter relay to operate. Upon operating, the busy relay R420 interrupts, at the contacts 422 and 423, a further point in the previously traced connection between the control conductors C382 and C393 oi the trunk 3| and completes, at the contacts 424, the previously mentioned path for applying ground potential to the control conductor C383 of the trunk 3 I. This application of ground potential to the control conductor C383 of the trunk 3| completes the previously traced multiple holding circuits for energizing the winding of the busy relay R360 in the secondary selector SSI and the winding of the stop relay R240 in series with the rotary magnet M259 in the primary selector PSI. Also the busy relay R420 completes, at the contacts 42|, a circuit for energizing the Winding of the test relay R365 in the secondary selector SSI, this circuit extending from ground by way of the contacts 42|, the control conductor C382 of the trunk 3|, the Wiper 315 and engaged contact in the associated contact bank 316 of the rotary switch 310 and the Winding of R365 to battery. When thus energized the test relay R365 operates, thereby to prepare, at the contacts 361, a circuit traced hereinafter for energizing the rotary magnet M319 of the rotary switch 310 and to complete, at the contacts 366, an obvious path for shortcircuiting the resistor 342. At this point it is noted that a normally completed series circuit for energizing the Winding of the test stop relay R345 and the test start relay R348 in the first distributor 66 is provided which includes a number of resistors arranged in series relationship and provided in the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors. The series resistance oi the above-traced circuit Ais suiiiciently high to prevent adequate energization of the test start relayR340 and the-.test .Sten relay @34s under. normal senr dirige-S: andthe resistente sillas Salies. einem lshst redeesdsumeientlr ini order te cartacee,- man` entregarse. 0f the, niedrige Pi ,the visst start relay R340 and the test stop relay R345 until several of the resistors provided in the secondary selectors are short-circuited, in a manner more fully explained hereinafter, the test start relay R340 and the test stop relay R345 being operated when the windings thereof are adequately energized.

Also upon operating, the answer relay R430 prepares, at the contacts 434, a. circuit traced hereinafter for energizing the winding of the storage relay R450 and prepares, at the contacts 435, a point in a chain circuit traced hereinafter for energizing the winding of the operator busy relay R400 in the common equipment for purposes more fully explained hereinafter.

The operator at the first B operator position 9| initiates the extension of the call to the called line in the exchange 20 by inserting the plug P545 of the cord circuit 1| into the jack terminating the desired called line. Thereafter, the position apparatus 93 associated with the first B operator position 9| causes ringing current to be projected over the called line and then operates further, thereby to disconnect the cord circuit lI from the position apparatus 93 in order to free the position apparatus 93 associated with the first B operator position 9| to receive additional calls routed thereto over idle ones of the cord circuits in the rst group of cord circuits from the A board in the exchange I0. When the position apparatus 93 is disconnected from the cord circuit 'II the answer relay R535 restores, thereby to interrupt the previously mentioned circuits for energizing the answer relays in the trunk circuits in the first group of trunk circuits in order to cause the answer relays to restore. More particularly, the answer relay R430 in the trunk circuit 5I restores to interrupt, at the contacts 434, a further point in the previously mentioned circuit ior energizing the winding of the storage relay R450 and to interrupt, at the contacts 435, a further point in the previously mentioned circuit for energizing the winding of the operator busy relay R400.

When the call is answered on the called telephone line in the exchange 20 a loop circuit is completed for energizing the winding of the battery supply relay R5|0 in the cord circuit 1|. This circuit extends from ground by Way of the right-hand winding of the battery supply relay R5I0, the winding 502 of the repeater 500 and the line conductors C55! and C553 to the plug P545; and from battery by way ol the left-hand winding of the battery supply relay R5|0, the winding 50| of the repeater 500 and the line conductors C550 and C552 to the plug P545, the plug P545 being connected by Way of the jack terminating the called line to a bridge path present between the line conductors of the called line. When this circuit is completed a connection is established between the calling line in the exchange I0 and the called line in the exchange 20, this connection including the calling line and the cord circuit 2|0 at the first A operator position II in the exchange I0, the trunk line TI and the primary selector PSI, the secondary selector SSI, the trunk circuit 5|, the cord circuit 'II and the called line in the exchange 20. Further it is noted that the line conductors C380 and 038| oi' the cord circuit 'II are connectedl to the windings and "504, oi the repeater 500;wl1ile the line ci?, ductors `C3550 andC55Io ,the cord circuit 'II arel connected to. fthe vgl'idings K50| v and 502 of the'repeater500, thewindings 50| `and, 502 of the ressentait est lederwaren@ tel-.ue

8 windings 503 and 504 thereof. Further it is noted that a signal current path is provided between the line conductors C380 and C38| of the cord circuit 'II, including the condenser 506 and excluding the windings of theY line relay R520; while a signal current path is provided between the line conductors C550 and C55I of the cord circuit '|I, including the condenser 505 and excluding the windings of the battery supply relay RI0.

Upon operating, the battery supply relay R5I0 interrupts, at the contacts 5I2, the previously mentioned circuit for illuminating the line lamp 1.541, thereby to indicate to the operator at the rst B operator position 9| that the call routed by way of the cord circuit 1I has been answered. Also the battery supply relay R5I0 interrupts, at the contacts SI2, a further point in the previously mentioned circuit for illuminating intermittently the answer lamp L546, the last-mentioned circuit being interrupted incident to the operation of the position apparatus 93 to disconnect the cord circuit 1| therefrom. Finally, the battery supply relay R5I0 completes, at the contacts 5H, an obvious path for short-circuiting the right-hand Winding of the line relay R520, thereby to reduce the resistance of the previously traced connection including the line relay R200 in the cord circuit 2|0 at the first A operator position II in the exchange I0, thereby to cause the line relay R200 to operate. Upon operating, the line relay R200 interrupts, at the contacts 2|, the previously mentioned circuit for illuminating the answer lamp L203, thereby to indicate to the operator at the first A operator position Il that the call has been answered on the called line in the exchange 20.

Reviewing now the operation of the trunk circuit 5I, it is noted that the busy relay R420 occupies its operated position, thereby to cause ground potential to be applied, at the contacts 424, to the control conductor C333 of the trunk 3| and to cause ground potential to be applied by way of the secondary selector SSI to the control conductor C264 of the trunk 2|. Also the operated busy relay R420 causes ground potential to be applied by way of the contacts 42| to the control conductor C302 of the trunk 3|. The application of ground potential to the control conductor C264 of the trunk 2| marks the trunk 2| and consequently the secondary selector SSIy as busy to each primary selector in the first group of primary selectors, thereby to prevent other of the primary selectors in the ilrst group of primary selectors from seizing the trunk 2|. The application of ground potential to the control conductor C383 of the trunk 3| marks the trunk 3|, and consequently the trunk circuit 5I and the cord circuit 1I individually associated with the rst B operator position 9|, as busy to the secondary selectors in the first group of secondary selectors, thereby to prevent any of the secondary selectors in the iirst group of secondary selectors from seizing the trunk 3| when another preselecting operation of the secondary selectors in the first group of secondary selectors is initiated, in a manner more fully explained hereinafter. Furthermore, the application oi ground potential to the control conductor C383 of the trunk 3| marks as busy any one of the secondary selectors in the first group of secondary selectors which has previously selected the trunk 3| prior to the operation of the secondary selector SSI in the iirst group of secondary selectors. Accordingly, at this time, each secondary selector in the first group of secondary selectors which has previously selected the trunk 3l prior to the operation of the secondary selector SS| in the iirst group of secondary selectors is marked as busy to the primary selectors in the corresponding groups oi primary selectors.

The application of ground potential to the control conductor C382 of the trunk 3| completes the previously traced circuit for energizing the winding of the test relay R355 in the secondary selector SSI in the first group of secondary selectors and the operating circuits of the test relays in the other secondary selectors in the first group of secondary selectors which have previously selected the trunk 3| prior to the operation of the secondary selector SSI in the iirst group of secondary selectors. Accordingly, at this time, the test relays in several of the secondary selectors in the first group of secondary selectors may occupy their operated positions, thereby to short-circuit the associated resistors in the corresponding secondary selectors in the first group of secondary selectors. More particularly, the test relays in a predetermined number of the secondary selectors in the first group of secondary selectors may be operated, thereby to cause the resistance of the previously traced series circuit for energizing the windings of the test start relay R340 and the test stop relay R345 to be appreciably reduced. More particularly, the test start relay R340 is of the marginal type and is so connected and arranged that it is operated when there are only two idle secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors which are available to be seized by the primary selectors in the first group of primary selectors and that it is restored when there are four or more idle secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the iirst group of primary selectors which are available to be seized by the primary selectors in the rlrst group of primary selectors. Furthermore, the test stop relay R345 is of the marginal type and is so connected and arranged that it is operated only when there are no idle secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the first group of primary selectors which are available to be seized by the primary selectors in the first group of primary selectors.

The release of the established connection between the calling line in the exchange I0 and the called line in the exchange 20 is under the control ci the respective lines. More particularly, when the connection to the called line in the exchange 20 is released the previously traced circuit for energizing the winding of the battery supply relay R5I0 is interrupted, thereby to cause the latter relay to restore. Upon restoring. the battery supply relay R5I0 recompletes, at the contacts 5|2, the previously mentioned circuit for illuminating the line lamp L54'I. The illumination of the line lamp L54'I indicates to the operator at the first B operator position 0I that the connection to the called line in the exchange 20 has been released, whereupon the operator at the first B operator position 9| takes down the connection by withdrawing the plug P545 of the cord circuit 1I from the jack terminating the called line. Also, upon restoring,

Vthe battery supply relay R5I0 interrupts, at the contacts 5II, the previously mentioned path for short-circuiting the right-hand winding of the line relay R520, thereby to increase the resistance of the loop circuit including the Winding of the line relay R200 in the cord circuit 2|0 at the first A operator position Il in the exchange I0, thereby to cause the line relay R200 to restore. Upon restoring, the line relay R2I0 completes. at the contacts 20|, the previously mentioned circuit for illuminating the answer lamp L203. The illumination of the answer lamp L203 indicates to the operator at the first A operator position I I that the connection to the called line in the exchange 20 has been released. The operator at the first A operator position II then takes down the connection to the trunk line TI by withdrawing the call plug P201 of the cord circuit 2I0 from the associated jack J I terminating the trunk line TI and by withdrawing the answer plug of the cord circuit 2I0 from the associated jack ter-- minating the calling line in the exchange I0.

When the call plug P201 is withdrawn from the jack J I, the previously traced loop circuit, including the windings of the line relay R520 in the cord circuit 1I, is interrupted, thereby to cause the line relay R520 to restore. storing, the line relay R520 interrupts, at the contacts 522, the previously mentioned circuit for illuminating the line lamp L541, thereby to indicate to the operator at the first B operator postion 9| that the connection from the A board in the exchange I has been taken down. Further the line relay R520 interrupts, at the contacts 52|, the previously mentioned circuit for energizing the winding of the busy relay R525, thereby to cause the lartter relay to restore and interrupt, at the conductor C363 of the trunk 3|, thereby to mark the trunk 3| as idle to fthe secondary selectors in the rst group of secondary selectors, and to interrupt the previously traced holding circuitA for energizing the Winding of fthe busy relay R360 and the previously traced holding circuit for energizing the Winding of the stop relay R240 in series with the rotary magnet M259. The busy relay R360 in the secondary selector SSI and the stop relay R240 in the primary selector PSI then restore. Upon restoring, the busy relay R360 prepares, at the contacts 362, a point in a circuit traced hereinafter for energizing the rotary magnet M319. Upon restoring, the stop relay R240 interrupts, at the contacts 246. a further point in the previously traced holding circuit for energizing the winding thereof in series with the rotary magnet M259. Also upon restoring, the busy relay R420 recocnpletes, at the contacts 422 and 423, the previously `traced connection between the control conductors C382 and C383 of the trunk 3|, thereby to cause bat, tery potential to be applied to the control conductor C363 of the trunk 3| and to the control conductor C264 of the trunk 2|. The application of battery potential to the conltrol conductor C383 of the trunk 3l marks the trunk 3| as idle to the secondary selectors in the rst group of secondary selectors; and the application oi battery potential to the control conductor C264 of the trunk 2| marks the trunk 2| as idle to the primary selec-tors in the rst group of primary selectors. Also upon restoring, :the busy relay R420 interrupts, at the contacts 42|, the

Upon reapplying ground p0. tential to the control conductor C362 of the trunk 3|, :thereby to interrupt the circuits for energizing the windings of the test relays in the various secondary selectors in the rst group of secondary selectors which have previously selected the trunk 3|. Upon restoring, the test relay R365 interrupts, at the contacts 366, the previously mentioned path for short-circuiting the resistor 342, thereby to increase 'the series resistance of the previously traced circuit for energizing in series the windings of the test start relay R340 and the test stop relay R345 of the first distributor 66. Further, the test relay R365 interrupts, at the contacts 361, a point in a circuit traced hereinafter for energizing the rotary magnet M319. At this time the apparatus in the exchanges |0 and 20 utilized in completing the previously traced connection are completely released and available for further use.

Considering now the operation of the first distributor 66, when there are only two idle secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors, the resistance of the previously traced series circuit for energizing the winding of the Itest start relay R340 and the winding of the test stop relay R345 is reduced suciently, thereby to cause operation of the test start relay R340. Upon operating, the test start relay R340 completes, at the contacts 34|, an obvious circuit for energizing the windings of the secondary selector start relay R335, thereby to cause the latter relay to operate. Upon operating, the secondary selector start relay R335 prepares, at the contacts 336. 331, etc., circuits for energizing the rotary magnets in the secondary selectors in `the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors. For example, at this time, the previously mentioned circuit for energizing the rotary magnet M319 of the rotary switch 310 included in the secondary selector SSI is completed only in the event the secondary selector SSI is idle and has previously selected a trunk extending to a trunk circuit which is now busy. More particularly, in the event the secondary selector SSI is busy due Ito the seizure thereof by a primary selector in the first group of primary selectors, the busy relay R360 occupies its operated position, thereby to intercontacts 362, a point in the previpreviously selected a trunk extending to an idle trunk circuit, the test relay R365 occupies its restored position, thereby to retain interrupted at the contacts 361, a point in the previously that the secondary selector SSI is operated incident to the operation of ithe secondary selector start relay R335 only in the event the busy relay R350 occupies its restored position and the test relay R365 occupies its operated position, which conditions prevail only in the event that the secondary selector SSI has not been seized by one of the primary selectors in the first group of primary selectors and trunk extending to a trunk circuit which is now busy.

Assuming that the busy relay R360 occupies its circuit for energizing thereby to condition the restored position and the test relay its operated position,

R335 occupies the previously mentioned the rotary magnet M310 is completed, this circuit extending from ground potential appearing upon the control conductor of the trunk previously selected by the rotary switch 310 and extending to a busy trunk circuit by way of the wiper 311 and engaged Contact in the as- .sociated contact bank 313 of the rotary switch 319, the control conductor C364 of the trunk 2|, the contacts 33|, 336, 352, 361 and 31-9, the rotary magnet M319 and the winding of the distributor start relay R350 to battery. When thus energized the rotary magnet M319 operates,

Wipers noted in the rotary switch 310 to be driven one step in the clockwise direction and to interrupt, 'at the contacts 310, the previously traced circuit for energizing the rotary magnet M319, thereby to cause the rotary magnet M319 to restore andtgo drive the Wipers noted of the rotary switch 31'0 one step in the clockwise direction. When this series circuit for energizing the rotary magnet M319 and the winding o the distributor start relay R350 is completed the distributor start re- 25 lay R350 does not necessarily operate, this relay being of the marginal type, and is operated only in the event it is energized in multiple with a number of other rotary magnets in addition to the rotary magnet M313, as explained more fully "L30 hereinafter.

When the wipers noted of the rotary switch 310 are driven one step in the rotary direction the next trunk extending to a trunk circuit is tested, in the manner previously explained. In the event this trunk is busy, further operation of the rotary magnet M313 is initiated; on the other hand, in the event this trunk is idle, further operation o the rotary magnet M310 is arrested. More particularly, in the event the trunk selected 4o by the rotary switch 310 is idle, no po-tential appears upon the control conductor thereof engaged by the Wiper 315 in the associated contact bank 315, thereby to interrupt the previously traced circuit for energizing the winding of the test re-l lay R335 in order to cause the latter relay to restore and interrupt, at the contacts 351, a point in the previously traced circuit for energizing the rotary magnet M319. Accordingly, at this time, the rotary magnet M319 is energized i" intermittent-ly until the rotary switch 310 is operated to select an idle trunk extending to an idle trunk circuit, at which time further operation of the rotary magnet M310 is arrested. Also it is noted that the other secondary selectors in the i' 55 various groups of secondary selectors accessible to the primary selectors in the first group of primary selectors are operated in a manner similar to the secondary selector SSI described above, thereby to cause each of the secondary selectors o0 in the various groups oi secondary selectors which are not seized by the primary selectors in the first group of primary selectors and which have previously selected trunk circuits which are now busy to be operated in order to preselect idie c5 trunk lines extending to idle trunk circuits,

In view of the above explanation of the mode of operation of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors, it will be understood that when four or more of the secondary selectors mentioned preselect idle trunks extending to idle trunk circuits the test relays in the secondary selectors restore, thereby to cause the resistance of the series circuit lor energizing the winding Vof the test start relay R340 and the test stop relay R345 to be increased sumciently in order to cause the Yteststart relay R300 to restore. Upon restoring,

the test start relay R300 interrupts, at the .contacts 34|, the previously mentioned circuit. for energizing the windings of the secondary selector start relay R335, thereby to cause the latter relay to restore in order to interrupt, at the contacts `335, 33], etc., further points in the previously mentioned circuits for energizing the rotary magnets in the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the first group of primary selectors. In View .of the above explanation of the mode of operation of the first distributor B5 in order to cause the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of prmary selectors to preselect idle trunk lines extending to idle trunk circuits, it will be understood that the other distributors operate in a similar manner in order to cause the secondary selectors in the various Vgroups of secondary selectors accessible to the primary selectors in the corresponding groups of primary selectors to select idle trunks extending to idle trunk. circuits.

Continuing now with the operation ot the iirst distributor 55, it is noted that the operation of the secondary selector start relay R335 may be effective to cause the circuits for energizing a large number of rotary magnets to be completed in multiple series, including the winding of the distributor start relay R350. In this event, the winding of the distributor start relay R350 is sufficiently energized, thereby to cause this relay to operate. Upon operating, the distributor start relay R350 completes, at the contacts 35|, an obvious circuit for energizing the upper winding of the switching relay R3 t0, thereby to cause the latter relay to operate and complete, at the contacts 3|5, an obvious holding circuit for energizing the lower winding thereof. Also the switching relay R3|0 completes, at the contacts 3|3, 3|4., etc., a number of multiple circuits for l energizing in multiple a number of groups of individual secondary selector cutoff relays. For example, the switching relay R3|0 completes, at the contacts 3|3, a circuit for energizing the Winding of the individual secondary selector cutoi relay R330 associated with the secondary selector SSL this circuit extending from ground by way of the resistor 3|8, the contacts 3|3, 03M and the winding of R330 to battery. When thus energized the individual secondary selector cutoff relay R330 operates. Similarly, the other individual secondary selector cutoff relays in the group, including the individual secondary selector cutoff relay R330, and in the other groups operate, thereby to prevent operation of the correspending secondary selectors. For example, upon operating, the individual secondary selector cutoff relay R330 interrupts, .at the vcontacts 33|, the previously traced circuit for energizing the rotary magnet M319.

Also upon operating, the switching relay R3||l completes, at the contacts 3H, an obvious circuit for energizing the upper winding oi the hold relay R210, thereby to cause the latter relay to operate. Upon operating, the hold relay R210 completes, at the contacts 212, a holding circuit for energizing the lower winding thereof, this circuit extending from ground by way of the resistor 256, the contacts 212, C292, the wiper 303 and engaged contact in the associated contact bank 304 of the rotary switch 300, C29| and the lower winding of R210 to battery. Also the hold relay R210 completes, at the contacts 21|, a circuit for energizing the rotary magnet M305, this circuit extending from ground by way of the contacts 21| and 28| and the rotary magnet M305 to battery. When thus energized the rotary magnet M305 operates to interrupt, at the contacts 306, a circuit traced hereinafter for energizing the winding of the step relay R215. Also, at the contacts 21|, the hold relay R210 completes a circuit for energizing the winding of the step relay R280, this circuit extending from ground by way of the contacts 21| and 210 and the winding of R280 to battery. When thus energized the step relay R280 operates shortly thereafter, the latter relay being of the slow-to-operate type. Upon operating, the step relay R280 interrupts, at the contacts 28|, the previously traced circuit for energizing the rotary magnet M305, thereby to cause the rotary magnet M305 to restore. Upon restoring, the rotary magnet M305 completes, at the contacts 306, the previously mentioned circuit for energizing the winding of the step relay R215, this circuit extending from ground by way of the contacts 21| and 306 and the winding of R215 to battery. When thus energized the step relay R215 operates to interrupt, at the contacts 216, the previously traced circuit for energizing the Winding of the step relay R200, thereby to cause the latter relay to restore. Upon restoring, the step relay R280 recompletes, at the contacts 28|, the p-reviously traced circuit for energizing the rotary magnet M305, thereby to cause the rotary magnet M305 to operate and interrupt, at the contacts 306, the previously traced circuit for energizing the winding of the step relay R215. Shortly thereafter the step relay R215 restores, this relay being of the sloW-to-release type, to recomplete, at the contacts 216, the previously traced circuit for energizing the winding of the step relay R280. Accordingly, the step relays R215 and R280 and the rotary magnet M305 interact in the manner described above, thereby to cause the rotary magnet M305 to operate and restore periodically, whereupon the wipers noted of the rotary switch 300 are driven step by step in the clockwise direction until the wiper 303 engages the Contact in the associated Contact bank 304 which is not connected to the conductor 020|. When the wiper 303 engages the contact in the associated contact bank 304 mentioned, the previously traced holding circuit for energizing the lower winding of the hold relay R210 is interrupted, thereby to cause the latter relay to restore in order to arrest further operation of the step relays R215 and R280 and the rotary magnet M305.

Also it is noted that, upon operating, the individual secondary selector cutoff relays R330, etc., interrupt the previously traced multiple circuits for energizing the winding of the distributor start relay R350, thereby to cause the latter relay to restore. Upon restoring, the distributor start relay R350 interrupts, at the contacts the previously mentioned circuit for energizing the upper winding of the switching relay R3l0, the latter relay being retained in its operated position due to the completed holding circuit for energizing the lower winding thereof at this time. When the wiper 30| engages the fourth contact in the associated contact bank 302, an obvious path is completed for short-circuiting the lower winding of the switching reiay am, thereby to cause the latter relay to restore and interrupt, at the contacts 3|5, the previously traced holding circuit for energizing the winding thereof. Also the switching relay R3|0 interrupts, at the contacts 3|3, 3M, etc., the previously traced circuits for energizing the individual secondary selector cutoff relays R330, etc., thereby to cause the latter relays to restore.

Considering now more particularly the operation of the rotary switch 300 in the rst distributor 66, when the wiper 30| engages the rst contact in the associated contact bank 302 a path is completed for short-circuiting the windings of the individual secondary selector cutoff relays in the group of relays including the relay R330, the switching relay R3|0 occupying its operated position at this time. This path extends from battery by way of the wiper 30| and engaged first contact in the associated contact bank 302 of the rotary switch 300, C3I5, the contacts 3|3, C3|4 and the windings of the individual secondary selector cutoff relays in the associated group to battery. Accordingly, at this time, only the individual secondary selector cutoff relays R330, etc., in the group mentioned restore, thereby to prepare, at the contacts 33|, etc., the previously traced circuits for energizing the windings of the rotary magnets M319, etc., in series with the distributor start relay R350. It is noted that the distributor start relay R350 is so connected and arranged that it will not reoperate when only the group of rotary magnets M319, etc., are operating. When the wiper 30| disengages the first contact and engages the second contact in the associated contact bank 302 of the rotary switch 300, the individual secondary selector cutoff relays in the previously mentioned group are reoperated and the individual secondary selector cutoff relays in the second group are restored, in a manner similar to that previously explained, thereby to cause operation of the rotary magnets in the correspending group.

In view of the above explanation of the mode of operation of the first distributor 66, it will be understood that, in the event operation of the rotary switch 300 is initiated, the various groups of rotary magnets are operated sequentially. This arrangement prevents the operation of the corresponding groups of secondary selectors from interfering with each other by preselecting the same idle trunk line extending to an idle trunk circuit. In other words, by causing the secondary selectors to operate in relatively small groups, the secondary selectors in the difierent groups preselect different idle trunks extending to corresponding different idle trunk circuits. This arrangement prevents excessive operation of the secondary selectors incident to operation of the first distributor 66 and causes intermittent operation of the rst distributor 66 to be less frequent than it would be in the event all of the groups of secondary selectors were allowed to operate simultaneously.

At this point it is noted that, ordinarily, operation of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the rst group of primary selectors will be arrested prior to completion of the operating cycle of the first distributor 66 due to the fact that the test start relay R340 restores when four or more secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the flrst group of primary selectors are rendered available to be seized by the primary selectors in the first group of primary selectors, as previously explained. Upon restoring, the test start relay R340 interrupts, at the contacts 34|, the previously mentioned circuit for energizing the winding of the secondary selector start relay R335, thereby to cause the lat ter relay to restore in order to arrest further operation of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the first group of primary selectors, as previously explained.

Also, in connection with the operation of the first distributor 6B, it is noted that when all of the secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the first group of primary selectors are rendered busy, due to actual seizure of the secondary selectors mentioned by the primary selectors mentioned, it is impossible for the first distributor 66 to assign idle secondary selectors in the various groups oi secondary selectors accessible to the primary selectors in the first group of primary selectors as all of the secondary selectors are busy at this time. Accordingly, in this event, the test stop relay R345 is operated in rder to complete, at the contacts 346, an obvious circuit for energizing the winding of the common primary selector cutoff relay R265. When thus energized the common primary selector cutoff relay R265 operates to interrupt, at the contacts 268, the previously mentioned path for applying ground potential to the control conductor C223, thereby positively to prevent operation of the primary selectors in the first group of primary selectors. Further the common primary selector cutoff relay R265 completes, at the contacts 261, an obvious connection between the secondary winding of the tone transformer 222 and the control conductor C224, the primary Winding of the tone transformer 222 being connected to a suitable source oi' tone current, not shown. The application of tone current to the control conductor C224 completes an obvious circuit for energizing the upper winding of the line relay R220 in the primary selector PSI and the line relays in the other primary selectors, thereby to cause the line relays mentioned to induce a corresponding tone voltage in the lower windings thereof which are connected to the trunk lines individually extending to the primary selectors in the iirst group of primary selectors. Accordingly, at this time, in the event one of the trunk lines extending between the exchange |0 and the exchange 20 and terminating in the primary selectors in the iirst group of primary selectors is seized at the A board in the exchange l0, busy tone will be produced in the receiver of the telephone instrument at the particular operator position at the A board, thereby to indicate to the operator at the particular operator position at the A board that all of the trunk lines in the iirst group extending between the exchange |0 and the exchange 20 are busy at this time.

When one of the secondary selectors in one of the groups of secondary selectors accessible to the primary selectors in the iirst group of primary selectors becomes idle, the test relay therein restores, thereby to cause restoration of the test stop relay R345 in the first distributor 66, in the manner previously explained. Upon restoring, the test stop relay R345 interrupts, at the contacts 343, the previously traced circuit for energizing the winding of the common primary selector cutor relay R205, thereby to cause the latter relay to restore. Upon restoring, the common primary selector cutoi relay R265 recompletes, at the contacts 256, the previously mentioned path for applying ground potential to the control conductor C233 and interrupts, at the contacts 251, the previously mentioned circuit for energizing the upper windings of the line relays in the primary selectors in the iirst group of primary selectors with tone current. When ground potential is reapplied to the control conductor C223 the primary selectors in the rst group of primary selectors are again rendered operative, in the manner previously explained,

Considering now the operation of the common equipment B5, when the operator at any B operator position, such, for example, as the first B operator position S I, is answering a call on one of the cord circuits in the associated group of cord circuits, such, for example, as the cord circuit 'Il in the rst group of cord circuits, the answer relay R535 in the position apparatus 93 occupies its operated position, thereby to cause the answer relays R430, etc., in the trunk circuits in the first group of trunk circuits to occupy their operated positions. The operated answer relays in the trunk circuits in the first group of trunk circuits mark these trunk circuits as busy, thereby to prevent the primary selectors in the various groups of primary selectors from selecting secondary selectors in the various groups of secondary selectors which have previously selected the trunk circuits in the first group of trunk circuits at this time, as previously explained. At this time, when the operator at the i'lrst B operator position 9| is busy, calls are routed to the operators at the other B operator positions to be answered.

When each B operator position at the B board in the exchange 20 is busy the previously mentioned chain circuit for energizing the winding of the operator busy relay R400 in the common equipment is completed, this circuit extending from ground by way of the contacts in at least one of the ltrunk circuits in each group of trunk circuits and the winding of R400 to battery. More particularly, the circuit for energizing the winding of the operator busy relay R400 includes the contacts 435 f the answer relay R430 in the trunk circuit 5 in the iirst group of trunk circuits individually associated with the rst B operator position 9|. When thus energized the operator busy relay R400 operates to complete, at the contacts 404, a circuit for energizing the winding of the switching relay R440 in the trunk circuit 5| in the first group of trunk circuits and to complete, at the contacts 403, 402, etc., similar circuits for energizing the windings of the switching relays in the other trunk circuits in the other groups of trunk circuits. When thus energized the switching relays in the trunk circuits in the various groups of trunk circuits operate in order to condition the trunk circuits in the various groups of trunk circuits to store a call, in a manner more fully explained hereinafter. The circuit'I for energizing the winding of the switching relay R440 in the trunk circuit 5| extends from ground by way oi the contacts 404, C4|5, the contacts 465 and the winding oi R440 to battery. When thus energized the switching relay R440 operates to interrupt, at the contacts 44|, the previously traced path for applying ground potential to the control conductor C383 of the trunk 3| and to complete, at the contacts 442, a path for applying battery potential by way of the winding of the storage relay R450 to the control conductor C383 of the trunk 3 I, this path extending from battery by Way of the winding of R450, the contacts 434, 442, 433 and 423 to the control conductor C383 of the trunk 3|. This operation of the switching relay R440 conditions the trunk circuit 5I to be seized by a primary selector in one of the groups of primary selectors over one of the secondary selectors in the first group of secondary selectors, in the manner previously explained. Accordingly, at this time, each trunk circuit in each group of trunk circuits is conditioned to store one call.

At this time, in the event the trunk 3| is seized over one of the secondary selectors in the first group of secondary selectors, such, for example, as the secondary selector SSI, ground potential is applied to the control conductor C383 of the trunk 3| incident to switching-through of the busy relay R360 in the secondary selector SSI, as previously explained, thereby to complete a circuit identical to that previously traced for energizing the winding of the storage relay R450. When thus energized the storage relay R450 operates to complete, at the contacts 455, a holding circuit for energizing the winding thereof, this circuit extending from ground by way of the contacts 455, 442 and 434 and the winding of R450 to battery. Also the storage relay R450 completes, at the contacts 455, a path for applying ground potential to the control conductor C383, this path extending from ground by way of the contacts 455, 433 and 423 to the control conductor C383 of the trunk 3|. This application of ground potential to the control conductor C383 of the trunk 3| marks the trunk 3| as busy to the secondary selectors in the rst group of secondary selectors having access thereto. Further the storage relay R450 completes, at the contacts 455, a circuit for energizing the storage relay in each other trunk circuit in the first group of trunk circuits, this circuit extending from ground by Way of the contacts 455 and 433, the multiple illustrated to each other trunk circuit in the rst group of trunk circuits and therefrom by way of the contacts corresponding to the contacts 433, 442 and 434 and the windings of the storage relays in the other trunk circuits in the first group to battery. Accordingly, the storage relays in the other trunk circuits in the first group are operated at this time, thereby to mark the other trunk circuits in the first group as busy to the secondary selectors in the various groups of secondary selectors having access thereto. Accordingly, it will be understood that the storage arrangement provided in the trunk circuits in the first group o1' trunk circuits and in the trunk circuits in the other groups of trunk circuits is so connected and arranged that only one call may be stored at this time in any trunk circuit in a given group of trunk circuits. Further the storage relay R450 prepares, at the contacts 45|, a point in a circuit traced hereinafter for energizing the winding of the storage busy relay R4|0 in the common equipment 65.

The previously mentioned circuit for energizing the winding of the storage busy relay R4||l in the common equipment 55 is completed when one call is stored in a trunk circuit in each group of trunk circuits and extends from ground by way of at least one of the trunk circuits in each group of trunk circuits, the control conductor C4IB, the contacts 40| and the winding of R4I0 to battery. More particularly, the above-traced circuit for energizing the winding of the storage busy relay R4I0 includes the contacts 45| of the operated storage relay R450 in the trunk circuit 5I in the first group of trunk circuits. When thus energized the storage busy relay R4I0 operates to complete, at the contacts 4|2, 4|4, etc., obvious circuits for energizing the windings of the common primary selector cutoi relays R265, etc., thereby to cause the latter relays to operate. Upon operating, the common primary selector cutoil. relay R265 prevents operation of each primary selector in the first group of primary selectors, in the manner previously explained; while the other common primary selector cutoii relays prevent operation of the primary selectors in the other groups of primary selectors. Accordingly, at this time, each trunk line between the exchange l0 and the exchange 20 is marked as busy by the presence of busy tone voltage thereon and operation of the primary selectors in the various groups of primary selectors is prevented.

Also the storage busy relay R4H) interrupts, at the contacts 4|I, 4|3, etc., obvious circuits for energizing the windings of the common secondary selector cutoff relays R325, etc., individually associated with the first distributor 66, etc. Upon restoring, the common secondary selector cutoff relay R325 completes, at the contacts 32B, obvious multiple circuits for energizing the windings of the individual secondary selector cutoff relays R330, etc., thereby to cause the latter relays to operate in order to prevent operation of the secondary selectors in the group of secondary selectors accessible to the primary selectors in the rst group of primary selectors. Similarly, the common secondary selector cutoff relays in the other distributors prevent operation of the other secondary selectors in the various groups of secondary selectors accessible to the primary selectors in the other groups of primary selectors. Accordingly, at this time. operation of all of the primary selectors in the various groups of primary selectors and operation of all of the secondary selectors in the various groups of secondary selectors are positively prevented.

After the operator at one of the B operator positions at the B board in the exchange 20, such, for example, as the first B operator position 9|, answers a call stored in a trunk circuit in the associated group of trunk circuits, such, for example, as the trunk circuit 5I in the first group of trunk circuits, the position apparatus 93 at the rst B operator position 9| is disconnected from the cord circuit `|I in the rst group of cord circuits individual to the trunk circuit 5I in the first group of trunk circuits, thereby to render idle the position apparatus 93 at the first B operator position BI and to cause the answer relay R535 to restore. Upon restoring, the answer relay R535 interrupts, at the contacts 535, the previously traced circuits for energizing the windings of the answer relays in the trunk circuits in the rst group of trunk circuits, thereby to cause the latter relays to restore. Upon restoring, the answer relays in the trunk circuits in the first group of trunk circuits interrupt the previously traced circuits for energizing the windings of the storage relays in these trunk circuits, thereby to cause the latter relays to restore. When the answer relay R430 and the storage relay R450 in the trunk circuit 5| restore, the trunk 3| extending to the trunk circuit 5| is marked as busy to the secondary selectors in the first group of secondary selectors having access thereto; while the other idle trunk circuits in the rst group of trunk circuits are marked as idle to the secondary selectors in the various groups of secondary selectors having thereafter, the control relay R425 being of the sloW-to-release type. Finally, upon operating, the start relay R460 completes, at the contacts 463, the previously mentioned circuit for energizing the winding of the operator start relay R405 in the common equipment 65, this circuit extending from ground by way of the contacts 463 and 426, C406 and the winding of R405 to battery. When thus energized the operator start relay R405 operates; and shortly thereafter the control relay R425 restores to interrupt, at the contacts 426, the previously traced circuit for energizing the winding of the operator start relay R405, thereby to cause the latter relay to restore. Accordingly, the operator start relay R405 remains in its operated position for a short time interval. Further it is noted that the operator start relay R405 is operated for a short time interval whenever the operator at any operator position 20 reoccupies her position after previously vacating it.

Upon operating, the operator start relay R405 in the common equipment 65 completes, at the contacts 406, 401, etc., circuits for energizing the windings of the secondary selector start relays R335, etc., in the distributors 66, etc., thereby to initiate operation of the various distributors. For example, the operator start relay R405 completes, at the contacts 406, an obvious circuit for energizing the winding of the secondary selector start relay R335 in the first distributor 66, thereby to initiate operation of the rst distributor 66, in order to cause the secondary selectors in the various groups ol'` secondary selectors accessible to the primary selectors in the iirst group of primary selectors which are idle and have previously selected trunks which are now busy to be reoperated in order to select idle trunks extending to idle ones of the trunk circuits in the varf ious groups of trunk circuits, in the manner previously explained.

Conclusions From the foregoing it is apparent that a telephone system is provided which comprises a first exchange provided with an A board and a second exchange provided with a B board and improved connected and arranged in order to trunk the calls straightforward exceedingly fast and in a simple and eflcient manner.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims al1 such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system, a B switchboard, a plurality of cord circuits associated with said B switchboard, a plurality of secondary selectors having access to said cord circuits, means for causing idle ones of said secondary selectors to preselect idle ones of rality of primary selectors having access to said secondary selectors, an A switchboard, a plurality of jacks at said A switchboard, a plurality of trunk lines individually associated with said primary selectors and individually terminating in at the B board in the exchange i.

said cord circuits, a plu- F said jacks, means at said A switchboard for routing a call over any one of said trunk lines by way of the corresponding one of said jacks, meansr controlled when a call is routed over said one trunk line for causing the associated one of said primary selectors to operate and select an idle one of said secondary selectors which has preselected an idle one of said cord circuits, thereby to route the call on said one trunk line straightforward to said B switchboard to be answered, means controlled when a call is routed over said one trunk line for rendering busy said one trunk line, means controlled when said one secondary selector is selected by said one primary selector for rendering busy said one secondary selector and said one cord circuit, and means controlled when all of said secondary selectors are rendered busy for preventing operation of all of said primary selectors and for rendering busy all of said trunk lines.

2. In a telephone system, a B switchboard including a plurality of operator positions, a plurality oi groups of cord circuits individually associated with said operator positions, a plurality of secondary selectors having access to said cord circuits, means for causing idle ones of said secondary selectors to preselect idle ones of said cord circuits, a plurality of primary selectors having access to said secondary selectors, an A switchboard, a plurality of jacks at said A switchboard, a plurality of trunk lines individually associated with said primary selectors and individually terminating in said jacks, means at said A switchboard for routing a call over any one of said trunk lines by Way of the corresponding one of said jacks, means controlled when a call is routed over said one trunk line for causing the associated one of said primary selectors to operate and select an idle one of said secondary selectors which has preselected an idle cord circuit in one of said groups of cord circuits, thereby to route the call on said one trunk line starightforward to the associated one of said operator positions to be extended, means at each of said operator positions for extending a call routed thereto, a plurality of normally ineffective blocking means individually associated with said operator positions, each of said blocking means being eiTective to prevent calls from being routed to the associated operator position, meansI controlled while a call is being extended from one of said operator positions for rendering,r effective the associated one of said blocking means, and additional means controlled while a call is being extended from each of said operator positions for rendering again ineffective each of said blocking means.

3. In a telephone system, a B switchboard, a plurality of cord circuits associated with said B switchboard, a plurality of secondary selectors havingr access to said cord circuits, a plurality of primary selectors having access to said secondary selectors, an A switchboard, a plurality of jacks at said A switchboard, a plurality of trunk lines individually associated with said primary selectors and individually terminating in said jacks, means at said A switchboard for routing a call over any one of said trunk lines by way of the corresponding one of said jacks, means controlled when a call is routed over said one trunk line for causing the associated one of said primary selectors to operate and select an idle one of said secondary selectors which has preselected an idle one of said cord circuits, thereby to route the call on said one trunk line straightforward to 

